a. Field of the Invention
The present invention pertains generally to microfluidic flow devices and specifically to mixers and splitters of microfluidic flow.
b. Description of the Background
The application of microfluidic analytical devices to chemical or biological assays has developed rapidly over the last decade. Although microfluidic devices have been highly successful, several performance limitations exist, notably reagent mixing.
Most mixing devices rely on diffusive mixing, wherein the natural laminar flow effects and the reagent's inherent diffusion coefficient cause the reagents to mix. Therefore, the mixing chamber/channel is usually extended to lengths that will ensure a completely mixed outlet stream. This approach may be acceptable for low flowrates, but high flowrates (>1 cm/s) or low analyte diffusion coefficients (<10−7 cm/s2) will require excessively long mixing channels. The difficulty in rapidly mixing reagents results from the fact that the system is restricted to the laminar flow regime (Re<2000) and also because the feature sizes are too small (typically <100 μm) to incorporate conventional mixing mechanisms.
The lack of turbulence in microfluidic systems has led to device designs that utilize multi-laminate, or flow splitting techniques to accomplish mixing in channels of shorter length. These designs split the incoming streams into several narrower confluent streams to reduce the mixing equilibrium time. Once mixing is complete, the narrow channels are then brought back together into a larger main channel for further transport, processing, and/or detection. The effectiveness of the flow splitting concept is based on the fact that the equilibrium time scales quadratically with the width of the channel. For example, if the width of the channel decreases by two, then the equilibrium time and the channel length decreased by a factor of four, or 25% of the original length. However, even a mixing length of 25% may still be unsuitable for some applications.
Other techniques for mixing may rely on active mechanical mixing, such as stirring paddles and the like. For very small fluidic passages, such devices are extremely fragile and difficult to manufacture.
It would therefore be advantageous to provide a device and method of mixing two confluent microfluidic laminar flows that did not require an excessively long channel to effectively mix the flows. Further, it would be advantageous to provide a splitting mechanism that may be able to split a stream of reagents into two streams of differing concentrations.